Some conventional transmitters transmit specially encoded signals using two or more antennas to improve the ability of a receiver to process these signals. For example, in some multiple-input multiple-output (MIMO) systems, Alamouti-encoded signals generated by a space-time encoder are transmitted to help increase decoding gain and reduce bit-error-rate (BER) at the receiver. In mobile environments, the transmitter and/or the receiver may be moving, causing the received symbols to be distorted by Doppler-shift. This distortion may reduce the receiver's decoding gain and may significantly degrade the receiver's BER, particularly at high signal-to-noise (SNR) levels.
Thus, there are general needs for receivers and methods for decoding received signals that may be distorted due to Doppler-shift. What are also needed are space-time decoders and methods that increase decoding gain in environments with high-Doppler shift.